1. Field of the Invention
The present invention relates to a toroidal type continuously variable transmission for use in, for example, a transmission for automobiles.
2. Related Background Art
An investigation has been made on utilization of a toroidal type continuously variable transmission, schematically shown in FIGS. 4 and 5, as a transmission for automobiles. Such a transmission to which the present invention is applicable is schematically shown in FIGS. 4 and 5. This toroidal type continuously variable transmission has an input side disk 2 supported concentrically with an input shaft 1 and an output side disk 4 fixedly attached to an end of an output shaft 3, as disclosed in Japanese Utility Model Application Laid-Open No. 62-71465. The inner surface of a casing which accommodates the toroidal type continuously variable transmission or a supporting bracket arranged in this casing is provided with trunnions 6 which swing about pivots 5 located at twisted positions with respect to the input shaft 1 and the output shaft 3, respectively.
Each of the trunnions 6 is made of a metal material having a sufficient rigidity and provided with the pivots 5 mounted on the outer surfaces of both ends, as shown in FIGS. 6 to 8. A circular hole 7 formed through a central portion of each trunnion 6 supports a base end of a displacement shaft 8 (see FIGS. 4 and 5) in a manner that an inclination angle of the displacement shaft 8 is adjustable by swinging the trunnion 6 about the pivot 5.
Around the displacement shafts 8 supported by the respective trunnions 6, power rollers 9 are rotatably supported. Each of the power rollers 9 is sandwiched between the input side and output side disks 2 and 4.
The inner surface 2a, 4a of the input side and output side disks 2, 4, opposite to each other, respectively have a cross-section which forms an arcuate concave surface, the center of which is located on the pivot 5. The outer peripheral surfaces 9a of the respective power rollers 9 formed in a spherical convex shape abut the inner surfaces 2a, 4a of the disks 2, 4, respectively.
A pressurizing unit 10 of a loading cam type is arranged between the input shaft 1 and input side disk 2 for resiliently pressurizing the input side disk 2 toward the output side disk 4. This pressurizing unit 10 is formed by a cam plate 11 which rotates together with the input shaft 1, and a plurality of (for example, four) rollers 13 retained by a retainer 12. On one side (the right side shown in FIGS. 4 and 5) of the cam plate 11, there is formed a cam surface 14 which presents an uneven surface in the circumferential direction. The outside (the left side, shown in FIGS. 4 and 5) of the input side disk 2 is also formed with a similar cam surface 15. Then, the plurality of rollers 13 are arranged for rotation about an axis in the radial direction relative to the center of the input shaft 1.
In operation of the toroidal type continuously variable transmission constructed as described above, when the cam plate 11 is rotated by the rotation of the input shaft 1, the plurality of rollers 13 are urged to the cam surface 15 on the outer surface of the input side disk 2 by the cam surface 14. As a result, the input side disk 2 is urged by the plurality of power rollers 9, and simultaneously with this, the pair of cam surfaces 14, 15 engage with the plurality of rollers 13, causing the input side disk 2 to rotate. Then, the rotation of the input side disk 2 is transmitted to the output side disk 4 through the plurality of power rollers 9, resulting in rotating the output shaft 3 fixedly attached to this output side disk 4.
Consider now that the rotational speed of the input shaft 1 and the output shaft 3 is changed. First, when the speed of the input shaft 1 and the output shaft 3 is decreased, the respective trunnions 6 are swung about the pivots 5 as shown in FIG. 4 to incline the respective displacement shafts 8 such that the outer peripheral surfaces 9a of the respective power rollers 9 abut a portion near the center of the inner surface 2a of the input side disk 2 and a portion near the outer periphery of the inner surface 4a of the output side disk 4, respectively.
Conversely, when the speed is increased, the trunnions 6 are swung as shown in FIG. 5 to incline the respective displacement shafts 8 such that the outer peripheral surfaces 9a of the respective power rollers 9 abut a portion near the outer periphery of the inner surface 2a of the input side disk 2 and a portion near the center of the input side surface 4a of the output side disk 4, respectively. If the inclination angle of the displacement shafts 8 is adjusted to be an intermediate value between those shown in FIGS. 4 and 5, an intermediate transmission gear ratio can be achieved between the input shaft 1 and the output shaft 3.
FIG. 9 shows a mechanism for inclining the trunnions 6 about the respective pivots 5 during a transmission operation, which is described in the specification of U.S. Pat. No. 4,928,542. Specifically, the pivots 5 are supported by needle bearings 16 so as to permit the pivots 5 to rotate and slightly displace in the axial direction with respect to a housing 17. For a transmission operation, pressure oil is supplied to a hydraulic cylinder 18 supported by the housing 17 to displace the trunnions 6 in the axial direction. Based on this displacement, the relationship of contact positions between the outer peripheral surfaces 9a of the power rollers 9 and the inner surfaces 2a, 4a (FIGS. 4 and 5) of the input side and output side disks 2, 4 is changed, causing the trunnions to swing about the respective pivots 5 in any direction.
Incidentally, a demand exists for reduction in weight and improvement in performance of the toroidal type continuously variable transmission constructed and operated as described above which may be incorporated in an actual transmission or the like.
On the other hand, the trunnions 6 for pivotally supporting the respective power rollers 9 are so heavy that the utilization of the trunnions 6 has constituted a restriction for reducing the weight of the toroidal type continuously variable transmission.
Specifically the trunnion 6 incorporated in a conventional toroidal type continuously variable transmission has a base 23 for supporting a base end of the displacement shaft 8 coupled to an intermediate portion of one side thereof and a pair of pivots 5 protruding from both end surfaces of the base 23. The base 23 is made from a cylindrical member of a material having a sufficient rigidity such as steel, and is formed with a recess 24 by machining an intermediate portion of one surface of the cylindrical member. In a circular hole 7 formed through the base 23 in a central portion of the recess 24, the base end of the displacement shaft 8 is inserted such that the displacement shaft 8 is freely coupled to and supported by the trunnion 6. The pivots 5 are arranged on both end surface of the base 23 coaxially with the base 23.
In the conventional trunnion 6 constructed as described above, since the center of the base 23 is coincident with the center of the pivots 5, useless portions may be included in a design for ensuring a withstandable load of the trunnion 6. In other words, the trunnion 6 tends to be heavier than is required.
For example, when the pivot 5 is applied with a force in the direction perpendicular to the central axis, this force is supported by plate members 25 which couple the base 23 to the pivots 5. However, peripheral portions of these plate members 25 indicated by a lattice pattern in FIG. 6 are almost useless for supporting these force and merely cause the total weight to be heavier.
When the displacement shaft 8 is applied with a force in the direction perpendicular to the central axis thereof through the power rollers 9, an inserted portion of the base end of the displacement shaft 8 with the circular hole 7 supports this force. For this purpose, it should be ensured that a sufficient thickness T, be provided to a body member 26 which is part of the base 23 and through which the circular hole is formed. However, when the center axis of the base 23 is coincident with the center axis of the pivots 5, the cross-section of the body member 26 becomes larger than is required. For this reason, not only the weight of the plate members 25 but also the weight of the body member 26 are so excessive that the trunnion 6 as a whole is too heavy.
Although it is of course possible to reduce the weight of the trunnion 6 by removing portions useless for improving the withstandable load, a process of selectively removing unnecessary portions is rather difficult and causes a higher manufacturing cost of the trunnion, so that it is not preferable.